1. Field of the Invention
The present invention relates to an apparatus for checking the diameter of a cylindrical part, rotating about a geometrical axis, e.g. an orbitally rotating crankpin, in the course of the machining in a numerical control grinding machine including a grinding-wheel slide, with a reference device for cooperating with the part to be checked, a measuring device movable with the reference device, a support device for supporting the reference device and the measuring device, the support device having a support element adapted to be fixed to the grinding-wheel slide, a first coupling element coupled to the support element so as to rotate about a first axis of rotation, and a second coupling element carrying the reference device and coupled to the first coupling element so as to rotate with respect to it about a second axis of rotation parallel to the first axis of rotation, a control device for controlling automatic displacements of the apparatus from a rest position to a checking condition, in the course of such displacements the reference device performing closing movements with respect to the support element, and a guiding mechanism associated with the reference device for guiding the arrangement of the latter on the cylindrical part towards the checking condition of the apparatus.
2. Description of the Related Art
Apparatuses with these characteristics, for the diameter checking of crankpins rotating with orbital motion about a geometrical axis, are disclosed in U.S. Pat. No. 6,067,721, assigned to the same assignee of this patent application. In particular, according to the embodiments shown and described in the above mentioned U.S. patent, the apparatuses have Vee-shaped reference devices that rest on the crankpin to be checked, and guide means associated with said Vee-shaped reference devices, for example with elements with suitably shaped surfaces for entering into engagement with the crankpin. The embodiments shown in U.S. Pat. No. 6,067,721 guarantee excellent metrological results and small forces of inertia, and the standards of performance of the apparatuses with these characteristics, manufactured by the assignee of the present patent application, confirm the remarkable quality and the reliability of the applications. However, in some cases there can be problems owing to the limited space available on the machine tool for mounting the checking apparatus including the guide elements that have surfaces with appropriate extension for guaranteeing the correct cooperation with the crankpin to be checked.
Object of the present invention is to provide an apparatus for the metrological checking of crankpins rotating in the course of the machining in a machine tool, for example during the in-process checking in a grinding machine for grinding crankpins rotating with an orbital motion, that can guarantee the same standards of performance, in terms of accuracy and reliability, as those of the apparatuses according to the above mentioned U.S. patent and offers small layout dimensions with respect to those apparatuses. This problem is solved by a checking apparatus of the hereinbefore mentioned type, wherein the guiding mechanism includes a limiting device with at least a pair of abutting surfaces adapted to engage with each other and limit the closing movements of the reference device during the automatic displacements towards the checking condition, and to disengage from each other further to the arrangement of the reference device on the cylindrical part to be checked. An advantage that the present invention provides is that, by virtue of the presence of the limiting device, the reference device is prevented from colliding against the grinding wheel in the event the apparatus is accidentally controlled to displace towards the checking condition and there is no crankpin on the worktable.